[3H]imipramine binding in the retinas of chickens and pigs

Dopamine D2 receptors are unevenly distributed in the rat hippocampus and are modulated differently than in striatum

The characteristics of dopamine (DA) D2 receptors were studied in rat hippocampus and for comparison in striatum using the [3H]spiperone radioreceptor assay in vitro. D2 receptors exhibit a bimodal distribution along the length of the hippocampus. Heterogeneity also exists in the transverse axis with high densities in the molecular layers of the subiculum and CA1 plus CA2. As in the striatum, D2 receptors in both dorsal and ventral hippocampus display high and low affinity states for agonists, but all three regions differ with regard to the percentage of receptors in these states. The modulation of these affinity states by GTP, Mg2+ and the iron-chelator, 1,1-O-phenanthroline, differs markedly between dorsal and ventral hippocampus, and between these regions and the striatum. A new model for the modulation of the affinity of D2 receptors for agonists is presented. These data suggest the presence of regional differences in the composition of the D2 receptor-regulatory protein complex.

[3H]serotonin binding sites in goldfish retinal membranes

Serotonin (5HT) binding sites were studied in goldfish retinal membranes by radioligand experiments. The binding site of [3H]5HT was sensitive to pre-treatment of the membranes at 40 degrees or 60 degrees C. 5HT and 5-methoxy-N,N-dimethyltryptamine were the best inhibitors of [3H]5HT binding to retinal membranes. The 5HT2 agonist, 1-(-naphthyl)piperazine, was also a potent inhibitor, however, (+)-1-2,5-dimethoxy-4-iodophenyl-2-aminopropane was less efficient. The catecholaminergic agents haloperidol and clonidine did not display an important inhibition. Propranolol, also reported as 5HT1B antagonist, was a relatively potent blocker. Monoamine uptake blockers did not show potent inhibition. The GTP analog, GppNHp, inhibited the binding. The iterative analysis of saturation curves revealed two classes of binding sites, a high affinity component (B(max) 2.45 pmol/mg of protein, kd 6.86 nM), and a low affinity component (B(max) 53.46 pmol/mg of protein, Kd 232.07 nM). Analysis of the association and dissociation kinetics suggested a binding site (Kd 2 nM). The semilogarithmic plot of the dissociation kinetics gave curves concave to the upper side. The selectivity of the binding and the inhibition by GppNHp suggest the existence of 5HT1 receptors in goldfish retina. The low affinity interaction probably represents the transporter of 5HT or a subtype of receptor expressed in glial cells.